Heretofore, SDH (Synchronous Digital Hierarchy) has been used as a digital signal optical transmission technology. Also, an APS (Automatic Protection Switching) control, which is stipulated in ITU-T Recommendation G.841, has been used as a ring protection technology of a ring network using SDH.
In a ring network, APS control is a technology to, in the case that a failure has occurred in a portion of the transmission path due to a disconnected fiber or the like, provide resolution of the failure. Optical transmission devices positioned at the nodes making up the ring network transmit/receive APS control information as a portion of the optical signals transmitted/received. The APS control information is control information including whether or not a failure has occurred in the ring network and information of nodes positioned on both ends of a transmission path that includes the location of the failure occurring (switching nodes).
The optical transmission devices receive optical signals including the APS information thereof, thereby recognizing that a failure has occurred, and the location of the failure. Also, the optical transmission devices positioned at the switching nodes indicated by the APS information executes ring switching processing of the signal transmission path. That is to say, in the case that the next transmission destination node of the received optical signal is another switching node, the optical transmission device provided on one of the switching nodes executes return processing of the transmission path, i.e. ring switching processing, to switch the transmission destination node so a transmission origin node of the received optical signal.
On the other hand, in recent years, as the amount of transmitted digital data has increased, high speed transmission technologies and wavelength multiplexing technologies such as WDM (Wavelength-Division Multiplex) have been advancing. According to the advancement of such optical transmission technologies, stipulations of optical signal (digital signal) formats have also been advancing, and in ITU-T Recommendation G.709, a transmission method called OTN (Optical Transport Network) has been standardized, a format definition corresponding to 100 Gb transmission has been stipulated, and APS control has been introduced also for same-format ODU headers.
Note that an optical transmission device has been disclosed, wherein in a WDM network, a current-use path used to transmit the optical signal and a backup path that corresponds thereto is provided for paths configured for each wavelength, and in the case that a failure is detected in a current-use path, a path switching function switches the path transmitting the optical signal to a backup path (see Japanese Laid-open Patent Publication No. 2000-209152 and Japanese Laid-open Patent Publication No. 2000-209244).